A surface-adsorbed monolayer of cap-shaped gold particles upon submicrometer-sized polystyrene spheres exhibits pronounced absorption in the visible region. When the surrounding refractive index was altered by immersion in a fluid, the direction of the shift in the absorption spectrum was dependent on the incidence angle of the irradiation. When a thiol molecule, known to adsorb selectively on gold upon polystyrene, was added, the resultant shift in the absorption spectrum's peak was consistently toward longer wavelengths. Consequently, at certain incidence angles, a change in the refractive index of the surrounding fluid produces no shift, whereas thiol adsorption results in a clear shift, apparently reflecting the different spatial regions in which the refractive index is altered by these two procedures.
© 2002 Optical Society of America
(160.3900) Materials : Metals
(240.6680) Optics at surfaces : Surface plasmons
(310.1860) Thin films : Deposition and fabrication
(310.6860) Thin films : Thin films, optical properties
(350.4990) Other areas of optics : Particles
Hiroyuki Takei, Michael Himmelhaus, and Takayuki Okamoto, "Absorption spectrum of surface-bound cap-shaped gold particles," Opt. Lett. 27, 342-344 (2002)